NASA to smash two probes into the moon today (Updated)

PASADENA, Calif. — Two NASA spacecraft have wrapped up their mission by intentionally crashing into the moon.
Engineers on Monday commanded the spacecraft to fire their engines and burn their remaining fuel. The first slammed into a mountain near the moon’s north pole. Its twin followed seconds later and aimed for the same target.
Since the impact site was in darkness, NASA had said the crash wouldn’t be visible from Earth.
The spacecraft named Ebb and Flow circled the moon for nearly a year, mapping the lunar gravity field. To do their job, they had to fly at low altitudes above the surface, which consumes a lot of fuel.
NASA decided to execute a controlled crash and bring the spacecraft down far away from any historical site on the moon.

But getting back to people who like smashing things into the moon, are you ready for the GRAIL mission’s demise this afternoon?

Back in January of this year two washing-machine sized probes — nicknamed Ebb and Flow by Montana school kids — linked up a couple of dozen miles above the surface of the moon. They spent most of this year zipping around the moon, in tandem, at 3,600 mph.

Now that their primary mission (see below) is accomplished, and they’re running out of fuel, NASA’s sending them out in style. By crashing them into the moon. They will impact an unnamed mountain near the moon’s north pole this afternoon.

This image shows the final flight path for NASA’s twin Gravity Recovery and Interior Laboratory. (NASA)

Alas, no video of the impact will be available because the impact site will be in shadow at the appointed hour, 4:28 p.m. CT (2:28 p.m. PT). Nevertheless NASA will provide commentary on the crash beginning at 4 p.m. CT with, you guessed it, streaming video of talking heads and graphics.

So what has GRAIL done?

Flying in formation, Ebb and Flow have been using radio signals to define the distance between them. As they fly over areas of lesser or greater gravity, this distance varies slightly, and this has allowed scientists to create a high-resolution map of the moon’s gravitational field.

An artist’s depiction of the twin spacecraft that comprise NASA’s GRAIL mission. (NASA)

This information will give scientists insights into what lies beneath the lunar surface, and in addition to enlightening us about the moon, it will tell us about the evolution of Earth and other rocky worlds in the inner solar system.